Instrument for measuring the resistance of electric circuits.



No. 688,058. Patented Dec. 3, |901. E. K. BBCWN.

INSTRUMENT FDR MEASURING THE'RESISTANCE 0F ELECTRIC CIRCUITS.

(Application led Apr. l, 1901.)

(I'In Model.)

UTED STATES PATENT OEEICE.

EDVARD K. BROWN,.OF SPRINGFIELD, MASSACHUSETTS.

.INSTRUMENT FOR MEASURING THE RESISTANCE OF ELECTRIC CIRCUITS.

SPECIFICATION forming part of Letters Patent N o. 688,058, dated December 3, 1901. Application filed April l, 1901. Serial No. 53,797. (No model.)

.To a/ZZ whom t may concern:

Be it known that I, EDWARD K. BROWN, a

citizen of the United States of America, re.

siding at Springfield, in the county of Hampden and State of Massachusetts, have invented new and useful Improvements in Instruments for Measuring the Resistance of Electric Circuits, of which the following is a specication.

This invention relates to instruments for measurement of electrical resistance, the object of the invention being to provide in a compact and portable form an instrument for theabove purpose whereby either one of two well-known methods may be employed for determining said resistance. These two methods are known one as the fall-of-potential or drop method and the other as the current method. In the rst of these methods the drop across the resistance to be determined is compared with the drop across a known resistance, and in the second method, which is used more particularly to measure high resistances, the current iiowing through a known resistance is compared with the current when the unknown resistance to be determined is inserted in series therewith. All of the apparatus being employed for the de` termination of resistances by the drop method referred to, the specification is directed and the claims drawn mainly to the device as thus employed. The use of the instrument for the measurement of resistance by the current method is also given as more clearly emphasizing the capabilities of the invention; and the invention consists in the construct-ion described in the following specification and clearly pointed out in the claims.

The drawing consists of a perspective view of a device embodying this invention, in which the fiat plate of insulating material on which the various circuits are supported is shown broken away. The drawing also shows in dotted lines a box of which said plate forms the cover, which box serves to inclose said circuits and a suitable portable battery.

A portion of a galvanometer only is shown in the drawing.

Referring now to the drawing, ma indicate a plate of insulating material, such as wood or hard rubber or similar substance, which forms a cover for a box-like body y. (Indicated in the drawing bydotted lines.) On said plate nearl one end thereof are mounted two binding-posts H H2, to whichare attached the two terminals of a circuit R, whose resistance is to be measured under the abovenamed drop method. On the opposite end of said plate x are two binding-posts H3 and H4, similar in all respects to said first-named binding-posts, and to these posts H3 and H4 may be connected the terminals of a circuit S,Whose resistance is to be determined by said second or current method. To the posts H2 and Hl two keys A and C are secured, which are of metal and extend toward the center of the plate 0c, their ends lying over-and normally out of contact with the contact-points A' and C'. Between these contact-points is located a third one, (indicated by B,). From a point on the side of the plate a: opposite to the contact-point B is a post to which a third key B is secured, whose free end lies over the contact-point B. On that side ofthe said platen@ opposite to the said contact-points are two binding-posts G and G2, to which are attached two swinging metal arms g and g2, whereby connections may be madewith the bindingposts zu of a galvanarneter/U. Between the posts G and H2 and connected therewith is the resistance F. It will be assumed that this resistance equals a certain unit of measure-say one ohm. From said binding-post G a line K runs to one pole of the battery E and from thence to the contact-postB. From the post Gf2 a line J runs to the post HS, thence to the contact-point C, and thence to the contact-point A. A line (indicated by D) runs from the post H to the post H4 and a line M from post H to the post L, by which the key Bis secured. This completes the various circuits.

The battery E may be of any suitable type, but the one generally used is the well-known chlorid-of-silver dry battery.

In operating this instrument to determine the resistance, for example, of a circuit R the instrument is first connected, by means of the arms g and g2, with the binding-posts w yw of the galvanometer o. The terminals of the circuit R are then secured to the binding-posts H and H2. Nowby pressing the key B the battery-circuit will be completed IOO and the current from the battery will iow through the line K, the key, the line M, to the post H', thence through the line R, whose resistance is to be determined, the resistance F, and from thence through K to the battery. It is thus seen that the line R and the resistance F are connected in this circuit in series. It will also be noted that the post G', to which one end of resistance F is connected in the above-named circuit, is also connected by the arm g' with one of the posts w of the galvanometer o. Now while holding down the key B if the key C is depressed a shunt-current will iow from post H' through the vline D to the key C and from thence through the line J to the binding-post G2, which, by means of the arm g2, is connected with the other post n: of the galvanometer. With these two keys held down to their contact-points the galvanometer will give a reading whose value depends upon the drop between the posts G' and H', containing the known resistance F and line R connected in series, as stated. If now the key C be released and the key A depressed, a shunt-current will flow from the post H2 through the key A, line J, post G2, arm g2, to the other post w ot the galvanometer @,whose value depends on the drop between the posts G' and Hwhich contain the known resistance F only. As the resistance of any part of a circuit carrying the same current is proportional to the drop between the terminals of that part, a comparison of the combined resistance of R and F with Fonly is obtained, and the resistance of R is found by deducting the known resistance F.

The above-described method is, as has been stated, usually the one which is employed for determining low resistances.

The instrument may also be used to determinehigher resistances bythe current method referred to, it desired, in which case the terminals of the circuit would be secured, respectively, to the posts H3 H4, and if the battery-key B be then depressed the current will flow from the battery E through line K, the key B, line M, post H', line D to H4, thence through the circuit S to H3, line J, through the galvanometer, and thence through K to the key again. The galvanometer will thus indicate a current flowing whose value depends upon the total resistance of the circuit, the known part consisting of the galvanometer and battery and the unknown resistance of line S. If now the key C be depressed while B is still in contact with B', the line S will be short-circuited, the current passing through the line M from B, through line D to the key C, and through O' and the line J to the galvanometer by means of the before-described connections gz. Its value .depends upon the resistance of the known portion only of the circuit. As the resistance' of a circuit depends, inversely, upon the current flowing, (the electromotive force being constant,) the total resistance will be to the known part as the current through the known part is to the current through the total. Subtracting the known resistance gives the resistance required.

From the above description it is apparent that the instrument described may be used with equal facility to determine resistances by either. ot the above-mentioned methods, the whole being in a compact and portable form. When not attached to a galvanometer, the arms g' and g2 fold in between the posts G' and G2 and may be held in that po- Y sition by tightening. up the .nuts on said post.

No reference has been made to the resistancev of the various connections between the battery and galvanometer and various keys or switches, for said resistance is too small to take into account.

Having thus described my invention, what I claim, and desire to secure by Letters Patent of the United States, is

l. In an instrument for measuring electrical resistance, a battery-circuit comprising abattery, a switch or key, a known resistance, terminals for the inclusion of resistance to be measured; a galvanometer-circuit, one end of which is directly connected to the battery end of the known resistance, comprising terminals for the inclusion of a galvanometer, and switches or `keys through which it may be connected in shunt to Various parts of the battery-circuit, substantially as described.

2. In an instrument for measuring resistance, a battery-circuit comprising a battery, a switch or key, terminals for the inclusion of a galvanometer, terminals for the inclusion of resistance to be measured, and a switch resistance to be measured, substantially as described.

3. In an instrument for the measurement of electrical resistance, a battery, a battery key or switch, two branches leading from said switch, one including a known resistance, and terminals for theinclusion of unknown resistance to be measured, and having keys or switches A, C, connected to the ends of known and unknown resistances respectively, for closing a shunt-circuit through a galvanometer; the second branch having terminals for the inclusion of said galvanometer, terminals for the inclusion of the resistance to be measured, and a key C for short-circniting the latter, substantially as described.

4. In an instrument for measuring electrical resistance, the combination with bindingposts in the branches of the galvanometercircuit, of strap-terminals for connection to the galvanometer which are pivoted to said binding-posts and adapted to be folded up when disconnected from the galvanometer, substantially as described.

5. An instrument for measuring electrical resistance comprising a base, a pair of terminal binding-posts for connection to unknown low resistances to be measuredja pair of terminal binding-posts for connection to unknown high resistances to be measured, a pair of ter- IOO Vor key for short-circuiting the terminals of IIO minal binding-posts for connection to a galvanometer, a spring-strap battery-key in circuit With one of the low-resistance terminal posts, a spring-strap key directly connected to the other 10W-resistance .terminal post, a connection between the first-named 10W-resistance terminal post and one of the high-resistance terminal posts, asprng-strap key directly connected to the last-named high-resistance post, a known resistance connected to the other low-resistance terminal post, and to one of the galvanometer terminal posts, a

contact-point for the battery-key, and a battery-circuit connecting it to the galvanometerf post to which the known resistance is connected, connected contact-points for the other strap-keys, and a connection between said contact-points last named, and the other highresistance post and remaining galvanometerpost, substantially as described.

` EDWARD K. BROWN. Vitnesses:

WM. H. CHAPIN, J. D. GARFIELD. 

